In an IaaS (Infrastructure as a Service) of which a cloud system provides, there is a technique to monitor a packet to occur in a tenant. For example, a provider of a cloud service installs an agent of the monitoring service in a virtual machine of the tenant which is provided to the user. And the agent acquires the packet that a virtual machine transmits and receives and performs the monitoring of the delay and the lost of the packet based on the packets which are acquired.
However, when installing the agent of the monitoring service on the virtual machine, the agent utilizes the resource of the virtual machine which is provided as the tenant. Accordingly, influence on performance of the virtual machine may increase with the increase of the agent. Further, there is a technique that the monitoring server which is installed the agent is prepared separately from the physical machine that the virtual machine operates and a relay device such as a switch performs a mirror of the packet, of which the virtual machine transmits and receives. Accordingly, the packet makes to reach the monitoring server. Therefore, it is possible that the monitoring server stores the packet (below called as mirror packet) which is performed the mirroring the packet of the virtual machine for the monitoring target.